A typical plasma display panel (PDP) includes a front panel and a rear panel, which oppose each other with a predetermined distance therebetween, and barrier ribs disposed between the front and rear panels. The barrier ribs, the front panel, and the rear panel define a plurality of cells, each of which functions as a display element. In a cell, two electrodes disposed on an inner surface of the panel are separated from each other with a dielectric layer therebetween. Application of an AC voltage between the two electrodes induces a discharge, which leads to light-emission from a phosphor screen disposed on the surfaces of the barrier ribs. The emitted light passes through the transparent panel, and images are thereby displayed.
In PDPs, the resolution and brightness of images depend upon the width of the electrodes, the pitch of interconnecting conductors, the transparency of the dielectric layers, and the like. Electrode patterns and interconnecting conductor patterns can be formed by screen printing.
Photolithography is also available as a method for forming finer patterns. In photolithography, photosensitive paste, i.e., conductive paste having photosensitivity, applied on the entire surface of a substrate is exposed through a predetermined mask and developed to form a pattern, and the pattern is burned to prepare a high-definition conductor pattern. These methods use photosensitive pastes containing conductive powder and photosensitive resin binders.
It is essential to decrease the reflection of external light at the electrodes disposed on the front panel in order to improve the display contrast. The reflection of external light can be most efficiently decreased by forming a low-transmittance and low-reflectance black layer on a front-panel-opposing surface of a high-reflectance metal electrode so that the electrode will appear black when viewed from the front panel of the display.
FIG. 1 shows an example structure of display electrodes disposed on a front panel of a plasma display. A black layer 10 for preventing the reflection of external light and increasing the display contrast is formed on each transparent display electrode 1 (composed of ITO or the like) for plasma discharge. Bus electrodes 7 (metal electrodes such as silver electrodes) are formed on the black layers 10 to decrease the resistance of the electrodes. The black layer is composed of a material having a high degree of blackness and conductive properties, e.g., ruthenium oxide disclosed in Japanese Unexamined Patent Application Publication No. 10-255670.
Although ruthenium oxide is an excellent material having both a high degree of blackness and conductive properties, ruthenium has a drawback in that it is expensive and has a metallic luster.
An object of the present invention is to provide a black paste for forming a black layer that exhibits a high contrast without using expensive ruthenium and a plasma display panel having the black layer. In the present invention, a material having a desired degree of blackness and a material having desired conductive properties are combined so that a black layer having a high degree of blackness can be obtained at low cost.